Harte-Hanks Communications Inc. plans to sell three daily Texas newspapers and divest itself of other operating units in the next few months, the company said. Other properties for sale include all seven of Harte-Hanks' cable-television systems, two television stations, one non-daily publication and a direct marketing operation. The operations being sold make up about 18% of the company's anticipated 1987 revenue, officials said. The price of the deal was not disclosed. San Antonio-based Harte-Hanks said the sale is expected to be completed by the spring of 1988.